1. Field of the Invention
The present invention concerns high resolution printing by ink jet printers. More particularly, the present invention concerns high resolution printing wherein a printer expands low resolution print data to high resolution print data and prints out an image based on the high resolution print data. Additionally, the present invention concerns high resolution printing in which an ink volume applied to print each target is changed between a forward and a reverse printing scan by a print head.
2. Description of the Related Art
Ink jet printers generally print images on a recording medium by a print head ejecting ink droplets onto the recording medium based on print data received by the printer from a host computer. A user commences the printing process by selecting a print command from an application program stored in the host computer. When the user selects the print command, a print driver is activated that generally presents the user with various printing options. One such option is to select an image quality, such as a low or high resolution image.
Selection of one of these image quality options affects the time required for the printer to print the image. For instance, a high resolution image generally takes longer to print than a low resolution image because the print data sent from the host computer to the printer is generally twice or four times that of low resolution data. As a result, the printing speed is substantially reduced due to a slower data transfer.
One way to reduce the printing time required for high resolution images is to reduce the amount of data transferred from the host computer to the printer. In this regard, several methods have been proposed.
One such method is to transfer low resolution print data from the host computer to the printer and then have the printer enhance the image resolution before printout. According to this method, the printer generally enhances one pixel of 300 dpi resolution data to four pixels of 600 dpi resolution data. However, the resultant image quality is not as good as if the image were originally generated at 600 dpi.
Another method to reduce the amount of data transferred is known as indexing the print data. An example of a current indexing method is depicted in FIGS. 1A through 1C. As seen in FIG. 1A, current indexing methods utilize 2-bit information to indicate one of four printing patterns of 600 dpi per one pixel of 300 dpi. For example, the 2-bit data xe2x80x9c00xe2x80x9d indicates pattern 1100, 2-bit data xe2x80x9c01xe2x80x9d indicates pattern 1101, etc. This 2-bit information indicating one pixel of 300 dpi, as seen in FIG. 1B, is transferred from the host computer to the printer. The printer then expands the 2-bit, 300 dpi data into single bit 600 dpi data based on the 2-bit pattern information. As seen in FIG. 1C, pattern 1115 is the resultant expanded 600 dpi pattern representing the original 300 dpi pattern 1105.
This indexing method provides better image quality than merely enlarging one pixel of 300 dpi data to four pixels of 600 dpi data as previously mentioned. Additionally, the amount of data transferred from the host computer to the printer is reduced by half since only 2-bit 300 dpi data is required to be transferred rather than 4-bit 300 dpi data or single-bit 600 dpi data. However, because this indexing method requires 2-bit information to be transferred, the amount of data transferred is still twice the amount that would otherwise be required if a 1-bit information transfer method were to be employed.
Current ink jet printers are also limited in their ability to produce high resolution images due to their ink droplet ejection processes. In this regard, current ink jet printers eject ink droplets with a fixed pixel pattern in both a forward and a reverse scan of the print head. The fixed pixel pattern remains constant in both the forward and reverse scans. As a result, the number of ink droplets that can be ejected per pixel, and as a consequence the image quality, is limited by the pixel pattern. Therefore, what is needed is an ink jet printer that is able to change the ink droplet pixel pattern in order to eject more ink droplets per pixel and therefore enhance the image quality.
Additionally, current ink jet printers generally eject ink droplets at a constant frequency. That is, the number of ink droplets ejected per pixel generally remains constant in both the forward and reverse scans. Therefore, the number of ink droplets that can be ejected per pixel is limited by the frequency. As a result, the image quality is also limited by the frequency.
Therefore, what is needed is an ink jet printer with the ability to enhance the image quality by changing the ink ejection frequency in order to increase the number of ink droplets ejected per pixel.
Furthermore, current ink jet printers have power source concerns for printing high resolution images. Generally, when more power is required to be provided to the recording head, the print head and its driving circuit are required to have the capability of performing at the higher power, thus requiring additional resources that result in inefficiencies. In ink jet printers, the amount of power required to be supplied to the recording head is a function of several factors, including the printed pixel pattern. Because the printed pixel pattern is fixed in current ink jet printers, any desired reduction in the power required to be supplied to the recording head is limited by the pixel pattern. Accordingly, what is needed is a method of printing a high resolution image with a reduced power requirement.
According to one aspect, the present invention addresses the foregoing and achieves high resolution printing in situation where a printer expands low resolution print data received from a host computer into high resolution print data using a predetermined pixel pattern. According to this aspect of the invention, the predetermined pixel pattern is changed in each of a plurality of printing scans. Transferring low resolution data reduces the amount of data required to be transferred from the host computer to the printer and therefore the time required to print a high resolution image is reduced. Additionally, changing the predetermined pixel pattern enhances the image resolution because the host computer can select a pattern that differs from scan to scan and can tailor the pattern to produce better results in any one scan.
Accordingly, in one aspect the invention is a recording method wherein a printer prints an image on a recording medium by performing a plurality of printing scans. The method comprises the steps of transferring low resolution print data from a host computer to the printer, the printer expanding the low resolution print data to high resolution print data with a predetermined pixel pattern, and changing the predetermined pixel pattern in each of the plurality of printing scans.
As a result of the foregoing arrangement, a high resolution image is printed but the printing time is reduced. This is because the expansion process occurring in the printer allows low resolution scan data to be transferred from the host computer to the printer rather than requiring high resolution data to be transferred, thereby saving printing time in the data transfer process.
Additional data transfer advantages are achieved by the invention providing for pattern information to be transferred from the host computer to the printer, whereby the printer uses the pattern information in the data expansion process. The pattern information is determined by the host computer based on input densities of the image in order to provide for a high resolution image. Accordingly, the host computer determines which pattern is required for each scan line to obtain a high resolution image. Therefore, the printer merely uses the pattern information provided by the host computer to expand the data, thereby resulting in additional efficiency in the data expansion process.
The invention also provides for changing the pixel pattern after the expansion process, thereby further enhancing the image resolution. According to the invention, the pixel pattern is changed by changing the number of ink droplets ejected by the print head in a target pixel. The number of ink droplets ejected by the print head is increased by changing a scanning frequency of the print head in any particular scan. As a result, the additional ink droplets further enhance the image resolution.
According to this aspect, the present invention is a recording system for printing data on a recording medium by performing a plurality of printing scans by a print head capable of ejecting at least one color of ink. The system comprises a driving means for driving the print head, and a changing means for changing an image resolution printed by the print head in each of the plurality of printing scans. According to the invention, the recording system performs either multiple forward scans (uni-directional), or multiple forward and reverse printing scans (bi-directional), wherein the changing means changes the image resolution by changing the ink amount ejected by the print head to each target pixel between each scan. The ink amount is changed by either changing the pixel pattern between each scan, or changing the number of ink droplets printed within each target pixel by changing the scanning frequency of the print head.
As a result of the foregoing arrangement, the image resolution is enhanced by increasing the number of ink droplets ejected within each target pixel.
In yet another aspect, the invention achieves high resolution printing by providing a recording apparatus for printing data on a recording medium by performing a plurality of printing scans with a print head having ink ejection nozzles for ejecting ink of at least a first and a second color. The apparatus comprises a driving means for driving the print head across the recording medium and to eject at least the first color ink and/or the second color ink onto the recording medium, and a control means for causing the driving means to eject the first color ink in high resolution and the second color ink in low resolution in a first printing scan by the print head, and causing the driving means to eject the second color ink in high resolution in a second printing scan by the printing head.
As a result of the foregoing arrangement, a first color ink, such as black ink, can be ejected in high density on the first scan in combination with low density color, i.e. CMY, ink. The color ink, i.e. CMY, is then printed in high density in the second scan. Accordingly, a high resolution image can be produced in color, yet sufficient amounts of color ink can be efected so as to ensure a color image with high contrast.
According to yet another aspect, the present invention achieves high resolution printing by providing a recording method for printing data on a recording medium, wherein a host computer transfers data to a printer that prints the data by performing a plurality of printing scans with a print head that prints with at least one color. The method comprises the steps of the host computer generating scan data for each of the plurality of printing scans, and the host computer performing a first image process or a second image process to each of the generated scan data, wherein the scan data processed in one of the first or second image processes is printed in each of the plurality of printing scans of the print head.
According to the invention, the first and second image processes are an output correction process for generating output density values based on corresponding input density values so as to achieve an overall uniformity in print density regardless of print head direction. Alternatively, the first image process is a process for printing scan data in low resolution by the print head, and the second image process is a process for printing scan data in high resolution by the print head.
As a result of the foregoing, a pixel pattern for printing a high resolution image is obtained. The process obtains an output density and the required number of ink droplets to obtain the high resolution image. This data is used by the host computer to determine a pixel pattern for printing the high resolution image, which is then transferred from the host computer to the printer, whereby the printer prints the image.
In yet a further aspect, the invention achieves high resolution printing by providing a method for processing image data to be printed by a printer that prints an image on a recording medium by performing a plurality of printing scans. The method comprises the steps of generating scan data for printing the image, organizing the scan data into a first group of scan data comprising data to be printed with black ink, a second group of scan data comprising data to be printed with ink other than black ink and to be printed in a first scanning direction, and a third group of scan data comprising data to be printed with ink other than black ink and to be printed in a second scanning direction opposite the first scanning direction. The first, second, and third groups of scan data are therefore processed to obtain corrected scan data.
According to the invention, the generated scan data is input density data. Based on the input density data, the method processes the data to obtain an output density and the number of ink droplets required to be printed for a target pixel to obtain the required image resolution. As a result of the foregoing, a pixel pattern for printing a high resolution image is obtained, which is then transferred from the host computer to the printer, whereby the printer prints the image.
In yet further aspects, the invention is a computer-readable medium storing computer-executable process steps of the foregoing image process method as well as a print driver for performing the image process.
In yet a further aspect, the invention is a recording apparatus for printing data on a recording medium by performing a plurality of printing scans with a print head having ink ejection nozzles for ejecting ink of at least a first and a second color. The apparatus comprises driving means for driving the print head across the recording medium and to eject at least the first color ink and/or the second color ink onto the recording medium, and control means for causing the driving means to eject the first color ink with a first power and the second color ink with a second power in a first printing scan by the print head, and causing the driving means to eject the second color ink with a third power larger than the second power in a second printing scan by the printing head.
As a result of the foregoing arrangement, less power is used to print the high quality image. Therefore, the required print head and driving circuit capabilities can be reduced.